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At least 451 records · Page 25
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NASA NTRS1981

A measurement of the hyperfine structure of CO-17

It is pointed out that the isotope of carbon monoxide, CO-17, has appreciable hyperfine structure caused by the electric quadrupole and the magnetic dipole interactions of the O-17 nucleus which has a spin of 5/3. During a radioastronomical study of the structure and dynamics of cold interstellar clouds, it was found that the Bok globule B335 had an extremely small velocity dispersion such that the hyperfine components are clearly resolved. A graph is provided which shows the antenna temperature (a measure of intensity) of the CO-17 emission as a function of frequency. The hyperfine constants and line frequencies were redetermined for the CO-17 J=1 yields 0 rational transition. The observation of CO-17 was carried out with a 7 meter Cassegrain antenna during 1979 and 1980. The CO-17 molecular line parameters are listed in a table.

Frerking, M. A.↗
NASA NTRS1981

Cometary material and the origins of life on earth

The role of cometary material in determining the environmental conditions of the prebiotic earth is reviewed. The organic synthesis pathways that occur in dense interstellar clouds and in comets are examined, and complex organic molecules believed to exist (amino acids, carboxylic acids, purines, pyrimidines and hydrocarbons) based on spectral detections of degradation products are noted. Estimates of the amount of terrestrial volatiles of cometary origin that may have been acquired in collisions during the early history of the earth are considered, and shown to dominate any estimated contributions to terrestrial carbon from other extraterrestrial sources. Current evidence that the origin and early evolution of life began about four billion years ago is discussed in relation to the cometary bombardment processes occurring at the time and the resultant shock waves, reducing atmospheres and reactive chemical species. It is thus concluded that comets contributed significantly to the processes of chemical evolution necessary for the emergence of life on earth.

Lazcano-Araujo, A.↗
NASA NTRS1981

Organic chemical evolution

The course of organic chemical evolution preceding the emergence of life on earth is discussed based on evidence of processes occurring in interstellar space, the solar system and the primitive earth. Following a brief review of the equilibrium condensation model for the origin and evolution of the solar system, consideration is given to the nature and organic chemistry of interstellar clouds, comets, Jupiter, meteorites, Venus and Mars, and the prebiotic earth. Major issues to be resolved in the study of organic chemical evolution on earth are identified regarding condensation and accretion in the solar nebula, early geological evolution, the origin and evolution of the atmosphere, organic production rates, organic-inorganic interactions, environmental fluctuations, phase separation and molecular selectivity.

Chang, S.↗
NASA NTRS1982

Gamma ray lines from buried supernovae

An investigation is conducted concerning the possibility that supernovae (SN), located in dense interstellar clouds, might become the sources of gamma ray lines. The SN progenitor, in such a case, has to be an O or B star so that its evolutionary lifetime is short, and an explosion inside the cloud is still possible. It is shown that, in principle, a measurement of the abundances in the ejecta is possible. Attention is given to the characteristics of a model, the expected luminosity of gamma-ray lines, and the study of specific numerical examples for testing the feasibility of the considered mechanism. On the basis of the obtained results, it is concluded that gamma-ray line production by collisional excitation in confined supernovae remnants may be quite important.

Morfill, G. E.↗
NASA NTRS1981

Interstellar chemistry - Polycyanoacetylene formation

It is argued that interstellar polycyanoacetylenes are formed not on dust grains by catalytic buildup or by dissociation of longer molecules, but rather by gas phase ion-molecule reactions. The primary evidence for this view is the detection of deuterated cyanoacetylene in an interstellar cloud. It is also argued that the relative abundance of successive homologs of polycyanoacetylenes rules out the grain catalysis theory.

Langer, W. D.↗
NASA NTRS1982

The far-infrared spectrum of the OH radical

It is thought likely that the study of spectral lines in the far-infrared might provide at least as much information about the physics and chemistry of the interstellar environment as radioastronomy. However, by comparison with the microwave region, the far-infrared is largely unexplored. There is a pressing need for good laboratory data to aid searches and assignments of spectra from the interstellar clouds and nebulae. Brown et al. (1981) have conducted a study of the laser magnetic resonance (LMR) spectrum of the OH radical in its ground state at far-infrared wavelengths. The present investigation is concerned with the computation of the frequencies of individual hyperfine transitions involving all rotational levels up to J = 4 1/2. The results of the calculation are presented in a table. The results are summarized in a diagram which shows the low-lying energy levels of OH. The frequencies of transitions between levels studied directly in the LMR spectrum are quite reliable.

Brown, J. M.↗
NASA NTRS1981

Organic compounds in meteorites and their origins

The current investigation represents an extensively updated version of a review conducted by Anders et al. (1973). The investigation takes into account the literature through mid-1980. It is pointed out that Type 1 carbonaceous chondrites (C1) contain 6% of their cosmic complement of carbon, mainly in the form of organic matter. Most authors now agree that this material represents primitive prebiotic matter. The principal questions remaining are what abiotic processes formed the organic matter, and to what extent these processes took place in locales other than the solar nebula, such as interstellar clouds or meteorite parent bodes. The problem is approached in three stages. It is attempted to reconstruct the physical conditions during condensation from the clues contained in the inorganic matrix of the meteorite. The condensation behavior of carbon under these conditions is determined on the basis of thermodynamic calculations. Model experiments on the condensation of carbon are performed, and the synthesized compounds are compared with those actually found in meteorites.

Hayatsu, R.↗
NASA NTRS1982

Acoustic waves in supernova remnants

When the Mach number of a supernova shock wave, propagating through the hot interstellar gas, is less than the critical value 2.76, the interaction of the shock with an interstellar cloud produces a reflected pressure pulse that propagates away from the cloud as an acoustic wave. A preliminary analysis indicates that about 4% of the energy of an exploding supernova shell is converted into such waves. When the postshock gas temperature exceeds 2 x 10 to the 6th K, waves as short as 6 pc are damped in less than a wavelength, returning the energy to the hot gas. Longer waves, especially at late stages, are less strongly damped, and are superposed in the hot gas to create a fluctuating magnetoacoustic field, with typical periods of about 100,000 years. In the warm neutral clouds at temperatures of about 8000 K these waves are rapidly damped by plasma slip (ambipolar diffusion), providing a heat source that may account for the temperatures of these clouds.

Spitzer, L., Jr.↗
NASA NTRS1983

The doubly excited autoionizing states of H2

Neutral doubly excited states of H2 lie in the Franck-Condon region at energies beyound 23 eV above the ground state of H2. These repulsive resonance states may autoionize yielding H2(+) + e(-), H + H(+) + e(-) or dissociate to neutral ground and excited H atoms or H(+) + H(-). These processes are important in determining the thermal balance of interstellar clouds and the chemistry of the Jovian atmosphere. The present investigation is concerned with ab initio calculations of 24 autoionizing states of H2 which have mostly the 2 Sigma u + and first excited 2 Pi u states of H2(+) as the core orbital near R = 1. 4a(0). Of the 24 states reported, 14 have not appeared previously in the literature. For four of the remaining ten states an energy at only a single internuclear distance has been previously reported.

Guberman, S. L.↗
NASA NTRS1982

Paradigm transition in cosmic plasma physics

New discoveries in cosmic plasma physics are described, and their applications to solar, interstellar, galactic, and cosmological problems are discussed. The new discoveries include the existence of double layers in magnetized plasmas and in the low magnetosphere, and energy transfer by electric current in the auroral circuit. It is argued that solar flares and the solar wind-magnetosphere interaction should not be interpreted in terms of magnetic merging theories, and that electric current needs to be explicitly taken account of in understanding these phenomena. The filamentary structure of cosmic plasmas may be caused by electric currents in space, and the pinch effect may have a central role to play in the evolutionary history of interstellar clouds, stars, and solar systems. Space may have a cellular structure, with the cell walls formed by thin electric current layers. Annihilation may be the source of energy for quasars and the Hubble expansion, and the big bang cosmology may well be wrong.

Alfven, H.↗
NASA NTRS1982

The Orion Nebula - Large-scale distribution of far-infrared and submillimeter line emission

Attention is given to the results of a study of radiative cooling in the interstellar clouds of the Orion Nebula through the emission of far-IR and submillimeter radiation. That the gas is 'clumpy' in the ionized region of the nebula is indicated by the far-IR observations of doubly ionized oxygen. With respect to the edges of the ionized region, the excitation temperature for the 3P1 state is 228 K and the observed emission can be plausibly associated with either ionization or shock fronts at the interface between the ionized and neutral region. Consideration is also given to the possibility of an ionized carbon halo, the turbulent state of the molecular cloud, and the need for further laboratory and theoretical analyses.

Harwit, M.↗
NASA NTRS1984

Cosmogony as an extrapolation of magnetospheric research

A theory of the origin and evolution of the Solar System which considered electromagnetic forces and plasma effects is revised in light of information supplied by space research. In situ measurements in the magnetospheres and solar wind can be extrapolated outwards in space, to interstellar clouds, and backwards in time, to the formation of the solar system. The first extrapolation leads to a revision of cloud properties essential for the early phases in the formation of stars and solar nebulae. The latter extrapolation facilitates analysis of the cosmogonic processes by extrapolation of magnetospheric phenomena. Pioneer-Voyager observations of the Saturnian rings indicate that essential parts of their structure are fossils from cosmogonic times. By using detailed information from these space missions, it is possible to reconstruct events 4 to 5 billion years ago with an accuracy of a few percent.

Alfven, H.↗
NASA NTRS1983

The structure and emission spectrum of a nonradiative shock wave in the Cygnus Loop

The ultraviolet spectrum of a Balmer-line filament located just outside the main body of optical filaments in the Cygnus Loop confirms the nonradiative shock wave theory for its origin. This theory is extended to include the hydrogen two-photon continuum, and the possibility of slow electron-ion equilibration in the postshock gas is considered. The shock velocity is inferred from the H-alpha profile. Comparison of model calculations with optical and ultraviolet spectra favors Coulomb equilibration behind a 170 km/s shock over models with rapid equilibration due to plasma turbulence. Elemental abundances in the preshock gas are found to be typical of diffuse interstellar clouds. The ram pressure behind the shock is higher than the pressures inferred for bright optical filaments. It is suggested that the bright optical filaments are regions of thermally unstable cooling behind shocks faster than the shock velocities inferred from their optical and ultraviolet spectra.

Raymond, J. C.↗
NASA NTRS1984

1E 0104.2 + 3153 - A broad absorption-line QSO viewed through a giant elliptical galaxy

The optical identification of the X-ray source 1E 0104.2 + 3153 is complicated by the close projection of a broad absorption-line (BAL) QSO (z = 2.027) 10 arcsec from a giant elliptical galaxy (z = 0.111) at the center of a compact group of galaxies. At only 1.2 de Vaucouleur radii (16 kpc for H sub 0 = 100 km/s Mpc) this QSO-galaxy projection is the closest yet discovered. Based upon current observations, the source of the X-ray emission cannot be conclusively determined. Present in the BAL QSO spectrum are extremely strong Ca II H and K absorption lines due to the intervening galaxy, the first optical detection of the cold interstellar medium in an elliptical galaxy. The strength of these lines (EW = 2 and 1 A) requires observation through several interstellar clouds in the line of sight to the QSO. By its proximity to the central regions of the elliptical galaxy and the relative distances of the galaxy and QSO, this QSO is a particularly good candidate for observing dramatic transient gravitational lensing phenomena due to halo stars in the foreground galaxy.

Stocke, J. T.↗
NASA NTRS1984

Interstellar O2. I - Abundance, excitation, and prospects for detection of O-16O-18 at radio frequencies

Molecular oxygen, O2, is predicted to be an important constituent of the interstellar gas, but it has not yet been detected in interstellar clouds. In this paper, the gas phase production and destruction of O2 are reconsidered, a non-LTE calculation of level populations at cloud temperatures is presented, and O2 column densities in diffuse and dark clouds are predicted. Ground-based detection of the 234 GHz line of O-16O-18 is shown to be feasible; if CO and O2 are comparable in abundance in clouds similar to the Taurus molecular cloud or in giant molecular clouds, the brightness temperature is predicted to be 0.1 K.

Black, J. H.↗
NASA NTRS1984

Recombination of electrons with H3(+) and H5(+) ions

A microwave afterglow-mass spectrometer apparatus is used to determine the dissociative recombination coefficients for capture of electrons by H3(+) and H5(+) ions as a function of electron temperature. At an ion and neutral temperature of 240 K, the coefficient for H3(+) is found to vary slowly with the electron temperature at first, decreasing from 1.6 x 10 to the -7th cu cm/s at an electron temperature of 240 K to 1.2 x 10 to the -7th cu cm/s at an electron temperature of 500 K; at electron temperatures ranging from 500 to 3000 K, the coefficient falls as the reciprocal of the electron temperature. It is noted that the results, which have an uncertainty of + or - 20 percent, agree satisfactorily over the common energy range (0.03-0.36 eV) with the recombination cross sections determined in merged beam measurements by Auerbach et al. (1977). Attention is also given to the implication of the results for modeling planetary atmospheres and interstellar clouds.

Macdonald, J. A.↗
NASA NTRS1983

Kinematics of supernova remnants in the Galaxy and LMC

The optical emission lines of six SNRs have been observed at very high angular and kinematic resolutions. Kinematic ion temperatures were derived, and evidence was found in shocked regions for Maxwellian microturbulence on scales approximately equal to or less than 0.01 pc, and for non-Maxwellian macroturbulence on scales greater than 0.1 pc. The widths of shocked regions in the Cygnus Loop and the existence of three types of spectral feature in the LMC remnants are discussed in terms of SNR evolution in cloudly interstellar media.

Shull, P., Jr.↗
NASA NTRS1984

Studies of radiative transfer in planetary atmospheres

Progress is reported in modeling cometary emission in the 18-cm OH transition with specific application and predictions for Comet Halley. Radiative transfer is also being studied in rough and porous media. The kinematics of the cold, dark interstellar cloud Li34N were examined, and CO monitoring of Venus and Mars continues. Analysis of 3.4 mm maps of the lunar surface shows thermal anomalies associated with such surface features as the Crater Copernicus, Mare Imbrium, Mare Nubium, Mare Serenitatis, and Mare Tranquillatis.

Irvine, W. M.↗